A plurality of the element chips are manufactured by dicing a substrate including a semiconductor layer and a protective layer. The substrate generally contains a plurality of element regions and a plurality of streets defining each of the element regions, in which a plurality of the element chips are manufactured by dicing the substrate with the streets removed. Patent Document 1 (JP 2005-064231 A or US 2005/0035100 A1) discloses a dicing process of the substrate by scribing (laser-scribing) a shallow portion of the substrate along the streets by radiating a laser beam and then by cutting the rest portion through the substrate along the streets by means of a cutting blade.
In the laser-scribing process, a pulsed laser beam is typically used to suppress a thermal impact. It has been known that when the pulsed laser beam is used in the laser-scribing process, a laser abrasion causes particulates called debris (which may be also called an undesired material) scattering from a surface of an object to be processed and again adhering on the same surface. However, when mechanically cutting the rest portion through the substrate as disclosed in Patent Document 1, the undesired material adhered on the streets cause substantially no adverse impact on a processing quality.
In the meantime, a plasma-dicing process has been recently proposed for dicing the substrate, in which the shallow portion of the substrate is scribed along the streets by the laser beam and the rest portion thereof is etched through the substrate by a plasma exposure. A source gas and a condition for generating the plasma may be selected in accordance with material and/or thickness of the object to be processed. This causes adverse impact on the processing quality with the undesired material adhered on the streets during the plasma-etching step.